Calling arrangement for radiotelephone circuits



April 16, 1935. E. R. TAYLOR 1- r Al.

CALLING ARRANGEMENT FOR RADIOTELEPHONE CIRCUITS Filed sept. 20, 1952 HW EL l uw NQ w mmm QE Nw NmmNds Y ATTORNEY Patented pr. 16, 1935 uNirE s'rArEs PATENT oFFieE CALLING rARltANGElWIENT FOR RADIO- TELEPHONE CIRCUITS Edmund R. Taylor, Mount Vernon, and Charles C. Taylor, Flushing, N. Y., assgnors to American Telephone and Telegraph Company, a corporation oi' New York Application September 20, 1932, Serial No. 634,062

10 Claims. (Cl. Z50-9) This invention relates to radio telephone sysof the speech circuit is also used to control the tems and more particularly to arrangements for alarm arrangements. calling operators at stations: equipped with echo The invention may now bemore fully under-` or singing suppressing devices. stood from the following description when read In operating a radio telephone circuit such for in connection with the accompanying drawing, 5

example asmay be used in a ship harbor, it Figure 1 of which shows the circuit arrangeessential that the technical operator in charge ment for one terminal of a radio system embodyof the controls of the system be in attendance ing the invention, and Fig. 2 of which shows a when communication is attempted but it is uncircuit arrangement which may be used for one economical and wasteful to require the undior more of the radio stations to be communicated 10,

vided attention of the technical operator with. throughout the entire period that service is' Referring to the drawing, Fig. 1 shows the offered. This is particularly true during certain circuit arrangement of one end of the radio teleperiods of the night and on holidays, when phone system Which will be called the shore relatively little trani@ is offered. lt is also desirterminal for descriptive purposes. Fig. 2 shows 15 able in the interest of economy, ease of operation the circuit arrangement of one of the radio staand freedom from maintenance to restrict the tions to be communicated with, which is called boat equipments to the simplest and most rugged a ship station for descriptive purposes. It will apparatus capable cf affording the desiredy operabe understood, of ooursethat the invention is tion. not to be limited to a ship-to-shore radio tele- 20 As is Well known, a radio transmitter and radio phone system. receiver may be connected by means of a com- Referring to Fig. 1, SL designates the tWobination of four-wire and two-wire circuits to wire line connecting the control station to the a tWO-Wile terminal at a Switching point where switchboard. The two-wire line SL is connected GenneetiOhS may be established by a Silvitchins through a hybrid coil HB1 to a transmitting path 25 operator between the radio channel and various TL1 and a receiving path RLl being balanced by telephone circuits. It is also well known that tera Suit-,able network NL The pathv TL1 and the minalampliiiers,voice-operated devices and other fouowng parts 0f the transmitting Circuit inapparatus under the ccntrcl'cf a technical cpcraclude the transmitting Yvolume control variable tar may bc associated with the four-Wire circuit attenuator Tvc, amplifier TA, hybrid coil HB2, so in such a manner that echoes and singing, which transmitting path TLz, transmitting path TLS, Tri-ight be Caused by radio 0I' Wile lille YU-Iilialf transformer T1, and radio transmitter RTi. The ances, are effectively eliminated, and radiation receiving path includes receiving amplifier Rez, by the radio transmit/tei 0f Signals leCeVed by radio receiver RRi, receiving path RLz, transthe radio receiver is prevented. 1 formers T3' and T4, resistance terminationV R'I'z, 35

In accordance With this inVentiOh, Circuit ai-y receiving volume control attenuatcr RVC, amrangements are provided whereby an alarm is plier RAI and receiving path RLL alltn'matially Operated at the C0ht10l pOSitiOli. In order that when transmission is taking place When Communication iS attempted in eithelA d` over either the transmitting or receiving path the 40 TeetiOn and Wheleby `all alarm iS Operated at the other path will be disabled, echo suppressor de- 40 SWtohbOaid O1' Switching Center When @Ommuhvices are associated with each path. The echo cation is desired between the radio stations and suppressor associated with the transmitting path a land telephone station. These functions are TLl comprises an amplifier-detector unit TAD, obtained Without requiring any aPDaratuSDeof well known type, with its input connected culiar to the alarm signal system at the Outlythrough variable attenuator TSC and band-pass i5 ing OiV heat IaClO Stations and only a small lter F1 to hybrid coil HB2 in conjugate relationamount of such apparatus'at the other stations. Ship with transmitting path TL2, the output of Circuit arrangements are alSO pleyided whereby amplier TA being balanced by a suitable netthe Switchboard Operator may, at Will, cause the work N2. The output of the amplifier-detector V operation of an alarm .at the control terminal unit TAD controls through master relay TM the 50 or technical operators position, over the normal relay TSS and TEHO for performing operations Speech tfanSmSSiOn path. In general the eCOnincident to the'blocking or disabling operations cmy of apparatus and simplicity or operation is whereby transmission is permitted in only one of obtained by novel circuit arrangements whereby the paths TLz and RLi at a time. Normally,

55. a part of the apparatusv provided for the control transmission path TL'z is disabled by the back 55' contacts of relay TSS, which short-circuit the conductors, and transmission from transmission path TL1 to the radio transmitter cannot take place. Blocking means comprising transformer arrangements T3 and Tr are associated between receiving lines RL1 and RLz. These disabling means comprise transformer arrangements which are so connected as to be balanced when the contacts of relay TEHO are opened, thereby preventing transmission through the transformer arrangements. When the contacts of relay TEHO are closed, however, the transformer circuits instead of being balanced are, in effect, connected so as to be parallel-aiding, thereby permitting transmission to take place readily. Normally, relay TEHO (which is controlled by the amplifierdetector TAD) is de-.energized so that the receiving path is unblocked to permit transmission to take place from receiving path RLz to the twowire line SL.

The input of an amplifier-detector arrangement RAD is connected through band-pass filter F3, receiving sensitivity control RSC and resistance termination RT1 to the secondary windings of transformer T4, so as to be effectively in series with the resistance termination RTz in the receiving path RL1, and hasin its output a relay RM, which when operated opens the control circuit from the amplifier-detector TAD to switching relays TSS and TEHO, thereby maintaining the transmitting path TLg blocked and receiving path RL1 unblocked when signal currents are being received from the radio receiver. Static or other interference is prevented from causing operation of relay RM during idle periods by the action of relay COD which maintains a short circuit on receiving path RL: whenever receiving carrier f2 is not present. As will be explained later in connection with Fig. 2, the distant or boat transmitters are so arranged that carrier frequency f2 is radiated only when communication from a boat to the shore is desired. The control circuit of relay COD includes the following: The input band pass filter F4 which passes substantially only carrier frequency f2 is connected in multiple with the input of radio receiver RR1 and the output of filter F4 is connected to the input of detector D, the D. C. output of which controls the operation of relay COD.

The operation of the apparatus so far described for signal transmission is as follows: Signal currents incoming over the two-Wire circuit SL pass through the hybrid coil HB1 and through the amplifier TA. Some of the energy enters the amplifier-detector unit TAD and causes relays TM, TSS and TEHO to be energized. Relay TSS removes the short circuit from transmitting line TLz, while relay TEHO, by opening its contact, causes the transformer arrangements Ta and T4 to block the receiving path. In the meantime a part of the energy passes from hybrid coil HB2 through transmitting paths TLz and TL: to radio transmitter RT1 and is transmitted on carrier frequency f1. The receiving amplifier-detector RAD associated with the receiving path cannot be actuated to disturb the circuit condition now existing because the receiving path is disabled in the manner already described.

If in the normal condition of the circuit, carrier frequency f2 modulated with signals is received through amplifier RAz, a part of the received energy passes through band pass filter F4 to detector D causing the operation of relay COD, which removes the short circuit from receiving path RLz. In the meantime the remainder of the received energy passes into radio receiver RR1 and is demodulated, the resultant signals pass through receiving path RLz and the transformer arrangements T3 and T4. A part of the energy passes through receiving amplifier RA1 and hybrid coil HB1 to the two-wire line SL. The remaining received energy passes through receiving sensitivity control RSC to the amplifier-detector RAD, to cause the operation of relay RM which opens the circuit controlled by the amplifier-detector unit TAD, thereby preventing energization of relays TSS and TEHO, so that the transmitting path is disabled and the receiving path remains unblocked so long as the signal currents are being received.

The apparatus and circuits employed at the ship station may be of several well known types, as, for example, those shown in Fig. 2 which shows an antenna normally connected to radio receiver RRz which is arranged to receive carrier frequency f1 and the radio transmitter RTz, arranged to transmit carrier frequency f2. The antenna may be switched from the radio receiver RRz to radio transmitter RTz in a well known marmer by relay AR which is controlled by key AK. The output of radio receiver RRQ is connected to operators receiver ORz and the input of radio transmitter RTz is connected to operators transmitter OIz. Accordingly, the operator at the ship station may normally receive signals transmitted on carrier frequency f1 and may transmit signals on carrier frequency f2 by operating key AK which enables radio transmitter RTz and disables radio receiver RRZ and carrier frequency ,f2 is radiated only when signals are to be transmitted from the boat.

The apparatus so far described relates to communication between the two-wire line SL and a. distant radio station. The additional equipment and circuits which are associated with the shore terminal in order to afford signal alarm features will now be described. Referring to Fig. l and the operation of the echo and singing suppressing means described above, it will be seen that relay TM must be operated whenever signals are transmitted from the two-wire line SL to the radio transmitter RT1 and that relay CODl must be operated whenever signals are transmitted from the radio receiver RR1 to the twowire line SL and hence one or the other of these two relays TM and COD must be operated whenever communication is attempted in either direction of transmission. Contacts of these relays are connected to suitable circuits and apparatus for producing an alarm whenever either of them is operated. Accordingly the alarm circuit includes the following: The left-hand contacts of relay TM, the lower contacts of relay COD, key K1, relays R3, R4 and R5, key K2 and bell or buzzer B2, for giving an alarm at the technical operators position and in addition key Ka, line DCL, relay R1, bell B3 and lamp L, for giving an alarm at the switchboard.

The operation of the circuit is as follows: the operation of either relay 'IM or relay COD connects ground to key K1 and short-circuits the winding of relay R3 which is normally operated as shown, if key K1 is in its normal position, that is, with contacts closed. Key K1 is provided so that the alarm arrangements may bc disabled when alarm operation is not desired. Relays Rs and R4 are made slow acting in a well-known manner such as short-circuited windings or the addition of a copper slug to the core in order that intermittent, short duration operations of relays 'TM and COD, such as might be caused by static, may not give an alarm.l To continue the circuit operation, relay R1 releases after a predetermined interval of time has elapsed and its contacts close, short-circuiting in turn the windings of relay R4. Aiter'a second predetermined interval of time relay R4 releases and its contacts close causing the operation of relay R5. This causes the inner lower Vcontacts of relay R5 to complete the circuit of bell or buzzer B2 giving an alarm. If key K2 is in the normal position with its contacts closed relay R5 will lock itself 1 operated through its upper contacts andthe alarm will continue until key K2 is operated to break the locking circuit. 1

The remainder of the circuit operationV required to operate the alarm at the switchboard is as follows: Relay R5 operating as' above closes its lower outer contacts connecting battery to4 line DCL and hence causing operation of relay R7 at the switchboard. Relay R1 closes its contact completing the circuit for bell B3 and lamp L giving an audible and visual alarm at that point. Key K3 is provided at the technical operators position so that the lower outer contacts of relay Rs may be short-circuited and an alarm given at the switchboard, if desired, When relay R5 is unoperated.

Other apparatus and circuits are provided as mentioned earlier to aiIord means whereby the switchboard operator may signal the technical operator at will. These arrangements include the following: Oscillator O1 which generates a frequency suitable for transmission through the system, a lower frequency oscillator O2, relay Re, key K4, all at the switchboard end of twowire line SL and condenser C and relay R1 which are tuned to the frequency of oscillator O2, relay Rz and bell B1 at the technical operators position. The output of oscillator O1 is modulated or periodically interrupted by relay Re Whose operation and release are controlled by the output of oscillator O2. When signaling is desired key K4 is operated connecting the modulated output of oscillator O1 to the two-wire line SL. This energy passes through line SL, hybrid coil HB1, transmitting path TL1, volume control TVC, ampliiier TA, hybrid coil HB2, sensitivity control TSC band pass lter F1 to amplifier-detector TAD Where it is demodulated to produce energy of the same frequency as oscillator O2. This demodulated energy passes through condenser C and the windings of relay R1 and since they are tuned to that frequency, causes the operation of relay R1. When relay R1 has been operated for a predetermined length of time relay R24 releases completing the operating circuit of bell B1 and giving an alarm. Relay R2 is made slow acting in order to prevent static, or noise which might cause momentary operation of relay R1, from giving an alarm. Band pass iilter F1 serves to exclude a large amount of noise and other interference from amplier-detector TAD and hence reduces the number of false operations of relays TM and R1. The alarm circuit is relatively immune to false operation by speech Waves since relay R1 is relatively insensitive to frequencies other than say 20 cycles on account of its tuning, and because the impedance of low pass iilter F2, shunted across it, is low for frequencies below 19 cycles and high for those above. Furthermore analysis of the relative strengths of the various frequencies produced by the detection or" speech Waves shows that those higher in frequency than 19 cycles are relatively weak and of short duration.

Thus those that do cause operation' of relay R1 seldom last long enough to permit relay R2 to release and energize the alarm bell. It will also be noticed that theshunting eiect of condenser C and relay R1 Will not adversely affect operation of relay TM since the shunt impedance may be made high at all except the resonance frequency;

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely diierent from those illustrated without departing from the spirit or" the invention as dened in the following claims.

What is claimed is:

1. In a radio telephone system a four-wire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and radio receiver, respectively, to a two-wire terminal, and means common to both paths and operative in response to the transmission of speech signals in either direction through the four-wire circuit to translate such speech signals into an audible signal having tonal characteristics unrelated to speech.

2. Ina radio telephone system a four-wire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and radio receiver, respectively, to a two-wire terminal, and means common to both paths and operative in response to the transmission of signals in either direction through the four-wire circuit to produce an indication and continue the same after said signals cease.

3. In a radio telephone system a four-wire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and radio receiver, respectively, to a two-wire terminal, means common to both paths and operative in response to the transmission of speech signals in either direction through the four-wire circuit to produce an indication at the two-wire terminal and continue the same after said signals cease.

4. In a radio telephone system a four-Wire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and radio receiver, respectively, to a two-wire terminal, switching devices one associated with one branch of the four-wire circuit and the other associated with the other branch of the four-wire circuit for preventing echoes and singing therein, and means common to both paths and operative by the switching devices to produce an indication at the two-wire terminal in response to the transmission of signals in either direction through the four-wire circuit.

5. In a radio telephone system a four-Wire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and radio receiver, respectively, to a two-wire terminal, a control position with means for controlling transmission in the four-wire circuit located remote from the two-Wire terminal, and means common to both paths and operative in response to the transmission of signals in either direction through the four-wire circuit to produce indications at the two-wire terminal and at the control position and continue the same after said signals cease.

6. In a signaling system a transmission circuit adapted to transmit telephone signals and terminating at a switching position, echo suppressing means associated with the transmission circuit and including devices, one responsive to transmission in one direction, and the other responsive to transmission in the other direction for preventing echoes therein, and common means operative by either device of said echo suppressing means to produce the same indication at the switching position regardless of which device is operated.

7. In a signaling system a transmission circuit adapted to transmit telephone signals and terminating at a switching position, special signal generating devices associated with the transmission circuit at the switching position, echo suppressing means located remote from the switching position and associated with the transmission circuit; said echo suppressing means having associated therewith means operating to translate speech currents and special signaling currents into translated currents having non-speech characteristics, means controlled by currents translated from speech currents for preventing echoes in said transmission circuit, and signal receiving devices operated by currents translated from signal currents produced by said special signal generating devices at the switching point, said signal receiving devices being unresponsive to telephone signals.

8. In combination, a speech transmission circuit, an ampliiler-detector with its input connected to said transmission circuit and its output connected to a plurality of devices each responsive to a different type of signal, one of which devices controls transmission conditions in said transmission circuit and another of which produces a signal having characteristics unrelated to speech.

9. In combination, a transmission circuit, an amplier-detector with its input connected to said transmission circuit and its output connected to a plurality of signal responsive devices, one of which is responsive to one band of frequencies and controls transmission conditions in said transmission circuit and another of which is responsive to another band oi frequencies to produce a signal having characteristics unrelated to speech.

10. In combination, a transmission circuit, an amplifier-detector responsive to a predetermined frequency band with its input connected to said transmission circuit and its output connected to a plurality of signal responsive devices, one of which is responsive to one band of frequencies and controls transmission conditions in said transmission circuit and another of which is responsive to another band of frequencies to produce a signal having characteristics unrelated to speech.

EDMUND R. TAYLOR. CHARLES C. TAYLOR. 

